1. Field of the Invention
The present invention relates to peptide and/or peptoid inhibitors derived from β2-glycoprotein I (“β2-GPI”) that can be used to prevent or inhibit damage from ischemia and reperfusion in various diseases and conditions.
2. Description of Related Art
A lack of blood flow (ischemia) and therefore lack of oxygen (hypoxia) to cells and organs results in cellular death and tissue damage; however, the return of blood flow (reperfusion) to the cell or organ significantly magnifies the tissue damage initiated by ischemia. Reperfusion injury of one tissue or organ may also result in tissue damage in other organs, sometimes resulting in multiple organ failure. Reperfusion injury was first identified as a critical care issue during the Vietnam conflict. Soldiers who had been shot in the abdomen survived their wounds and avoided sepsis, but eventually died on Days 5-7 due to pulmonary complications. Since this time, research has shown that the pulmonary complications were due to an excessive immune response in the intestine which sends the inflammatory cells to other mucosal organs, primarily the lungs. As the mortality rate for mesenteric ischemia/reperfusion (“IR”) remains at 70-90% today, therapeutic development for this ailment is desperately needed.
Numerous other clinical conditions result in IR-induced injury ranging from myocardial infarction, cardiac bypass surgery, stroke, and organ transplantation. In addition, hemorrhage, heat shock, and burns frequently lead to decreased blood flow to the non-vital intestine. These clinical conditions are significant, as approximately 15,000 transplants and 30,000 cases of intestinal IR (mortality rate of 60-80%) occur each year in the United States. In addition, myocardial infarction and stroke are two of the leading causes of death in the U.S.
In the last two decades, the complement system of the innate immune response has been identified as the blood component responsible for such tissue damage. Although a number of existing complement inhibitors have been shown to provide effective therapy in several animal models, there is no approved drug for treating mesenteric ischemia/reperfusion or multiple organ failure in humans or other mammals. Research therapeutics for mesenteric IR include complement inhibitors and peptides to non-muscle myosin. Complement inhibitors prevent a broad spectrum of the innate immune response, but can only be used short-term, as the decrease in immune response also renders the patient unable to respond to bacteria, which can be particularly dangerous in treating intestinal damage where translocation of bacteria is highly likely. Non-muscle myosin peptides only recognize intra-cellular components, which means that the cellular injury must have already begun. In addition, there is limited evidence that the inflammatory response is actually attenuated.
Seminal studies on IR have determined that during reperfusion, complement activation is initiated by naturally occurring antibody (NAb) recognition of newly expressed antigens (neoantigens). Produced by peritoneal B1a B cells, IgM and IgG3 NAbs recognize multiple phospholipid binding proteins including the serum protein, β2-glycoprotein I (“β2-GPI”). β2-GPI, also known as apolipoprotein H, is a member of the complement control protein family but does not exhibit any known complement regulating function. As used herein, references to β2-GPI are intended to include apolipoprotein H. With five complement regulatory domains, β2-GPI exists in several conformations that are stabilized by carbohydrate moieties. Each conformation is proposed to have distinct biological activity. After binding anionic phospholipids, β2-GPI undergoes conformational changes allowing NAb recognition and binding of β2-GPI. However, β2-GPI is also a cofactor for plasminogen activation and an opsonin for the clearance of apoptotic cells by phagocytes. By binding to anionic phospholipids, DNA or other negatively charged molecules, β2-GPI is a major antigenic target for anti-phospholipid antibodies found in the serum of anti-phospholipid antibody syndrome (APLS) and systemic lupus erythematosus patients. Accordingly, increased anti-β2-GPI antibody titers correlate with increased risk of ischemic stroke or heart disease in APLS or systemic lupus erythematosus patients, respectively.
Our previous work demonstrated that during reperfusion β2-GPI binds to ischemic cell membranes allowing antibody recognition necessary for complement activation and inflammation. Using an in vitro model, anti-β2-GPI antibodies recognized β2-GPI bound to the surface of hypoxic endothelial cells, and β2-GPI binding to damaged ischemic intestinal tissue correlated with tissue injury (Fleming, S. D. et al., J. Immunol. 185:6168-6178 (2010)). As discussed in more detail below, it has been found that peptides derived from β2-GPI sequence attenuated intestinal damage and inflammation. Recent evidence also indicates that the mechanism of tissue injury is similar between reperfusion damage in the intestine, liver, and lungs, suggesting that the peptides may be useful therapeutics for these tissues as well.
Additionally, it has also been found that β2-GPI peptides may be of therapeutic value in chronic ischemic conditions. One prominent example of chronic ischemia occurs in cancerous tumors. As cancer progresses, the tumor becomes invasive leading to metastasis. Hypoxia plays a major role in tumor metastasis. It affects not only the autonomous tumor cell functions like cell division and invasion, which play a role in genetic instability and therapy resistance, but also the non-autonomous processes like angiogenesis, lymphangiogenesis, and inflammation, which all contribute to metastasis. Such malignant tumors account for about 12% of all deaths worldwide. During metastasis, changes occur within the tumor and in the surrounding tissue promoting additional cancer progression. The internal tumor changes include genetic, epigenetic and metabolic transformation, while externally, the microenvironment undergoes a significant modification. Specifically, the microenvironment becomes acidic, hypoxic, and inflamed leading to angiogenesis (formation of new blood vessels) and increased microparticle shedding into the blood stream. Tumor growth requires angiogenesis, which is the formation of new blood vessels. Angiogenesis provides oxygen and nutrients to growing tumor cells and is induced by a number of factors including endoglin and vascular endothelial growth factor (VEGF). In the present work, we hypothesized that β2-GPI-derived peptides may attenuate angiogenesis and tumor growth.